Cellular function depends on highly specific interactions between biomolecules (proteins, RNA, DNA, and carbohydrates). Alpha-helices, ubiquitous elements of protein structures, play fundamental roles in many of these interactions. Alpha-helix mimetics that can predictably disrupt these interactions would be invaluable as tools in molecular biology, and as leads in drug development. We have succeeded in creating a general approach for the synthesis of short stable alpha helices that can target chosen biomolecular interactions. Our strategy involves replacement of one of the main chain hydrogen bonds in the target alpha-helix with a covalent bond. The internal placement of the crosslink makes it possible to take advantage of the full helix functionality for molecular recognition. We have demonstrated that this new method results in unusually stable artificial alpha-helices. In this application, we explore the utility of these artificial helices for targeting complex signaling networks. With regards to specific aims, (1) We will create a conformationally and metabolically robust family of HBS helices. (2) We will construct a database of experimentally determined structures of helix-mediated protein-protein interactions and determine hot-spot residues in the helical protein interfaces. (3) We will develop structure-based ligands to help decode the GTPase signaling networks, and evaluate a new paradigm for discovery of specific inhibitors of protein kinase activity. Combined these three aims will offer rationally designed inhibitors of protein- protein interactions, and validate our design principles that are rooted in the fundamental theories of biophysics and physical organic chemistry. PUBLIC HEALTH RELEVANCE: Selective modulation of protein-protein interactions is a grand challenge for chemists and biologists. The ability to systematically modulate protein-protein interactions would greatly facilitate the discovery of candidate therapeutic agents for a broad range of diseases. The proposed research offers a synthetic method for developing artificial alpha-helical ligands for targeting chosen protein interfaces.